1. Field of the Invention
This invention relates to a process for prolonging the shelf life of fresh vegetables. More particularly, it relates to prolonging the shelf life of fresh root crops. This invention especially relates to prolonging the shelf life of carrots by a variety of processes each of which may include one or more of the following operations: a hot water treatment, a cooling step, exposure to vacuum, a coating operation, and a packaging operation.
2. Description of the Prior Art
Fresh fruits and vegetables are extremely perishable commodities. Heretofore many techniques have been employed to protect such food products from oxidative degradation, mold attack and moisture change and to preserve the freshness, texture and color of the fresh produce. One of the earliest means of lengthening the shelf life of fruits and vegetables was refrigeration. However, most fresh produce when stored under reduced temperatures for prolonged periods shows adverse effects on the taste, odor or quality of the product from microbial and mold growth above 35.degree. F. In addition, storage temperatures below 35.degree. F. often show chill injury to the tissue of the produce. Hence, in many instances refrigeration alone is not effective in achieving the desired shelf life for a particular fruit or vegetable.
Coating fresh fruits and/or vegetables is another of these techniques which has been employed with varying degrees of success. Not only must the coating be effective in prolonging the useful shelf life of fresh product, but the appearance of the commodity must not be altered from that of its natural state. At a minimum, this natural appearance must not only remain unchanged but should ideally be enhanced especially when the fruit or vegetable will be displayed for sale. The selection of a coating material is further complicated where the fruit or vegetable is to be consumed in its natural state and it is considered essential that there be no need to remove the coating. In that event, the coating material must not only be edible, it should not affect or alter the natural organoleptic characteristics of the fresh fruit or vegetable.
Typical of these prior art coatings are the wax emulsions of U.S. Pat. Nos. 2,560,820 of Recker and 2,703,760 of Cunning. Coatings of natural materials have been employed including milk whey (U.S. Pat. No. 2,282,801 of Musher), lecithin (U.S. Pat. Nos. 2,470,281 of Allingham and 3,451,826 of Mulder), gelatin together with polyhydric alcohol (U.S. Pat. No. 3,556,814 of Whitman et al.) and protein (U.S. Pat. No. 4,344,971 of Garbutt). Polymers have also been used extensively, viz., a thermoplastic polymer (U.S. Pat. No. 2,213,557 of Tisdale et al.), vinyl acetate polymer (U.S. Pat. No. 3,410,696 of Rosenfield), a hydrophilic polymer (U.S. Pat. No. 3,669,691 of De Long et al.) and the combination of a water soluble polymer and hydrophobic material (U.S. Pat. No. 3,997,674 of Ukai et al.). Cellulosic materials have found utility in coating fruits and vegetables including hydrated cellulose (U.S. Pat. No. 1,774,866 of Beadle), a combination of cellulose and wax (U.S. Pat. No. 2,364,614 of Beatty), cellulose ether in combination with a fatty acid ester (U.S. Pat. No. 3,471,303 of Hamdy et al.) or monoglyceride and a fatty acid metal salt (U.S. Pat. No. 3,461,304 of Hamdy et al.), or a sucrose ester of a fatty acid (U.S. Pat. No. 4,338,342 of Tan et al.).
Food preservation has for many years employed such mutually exclusive processes as dehydration and freezing. Both of these operations often include a heat treatment, known as blanching, which is conducted prior to the dehydration or freezing step. Blanching is said to reduce enzyme or bacteria level and to prevent or minimize undesirable changes during storage in the dry or frozen state, such as changes in color, odor or texture or loss of vitamins. Blanching may be conducted with steam (e.g., U.S. Pat. No. 2,373,521 of Wigelsworth), hot water (U.S. Pat. No. 2,515,025 of Vahl et al.), hot oxygen-free gas (U.S. Pat. No. 3,801,715 of Smith et al.) or hot air (U.S. Pat. No. 3,973,047 of Linaberry et al.).
U.S. Pat. No. 2,780,551 of Guadagni is also concerned with the preservation of raw fruits or vegetables by freezing. A heat pretreatment is employed here also, but it is a mild heat treatment to cause partial enzyme inactivation. The mild heat treatment may be conducted by immersing the food in a liquid which is heated to a temperature in the range of 150.degree. to 212.degree. F. for a period of from about 10 seconds at the higher temperatures to about 10 minutes at the lower temperatures. The heat treatment is described as heating the food at a temperature and for a period of time sufficient to inactivate the enzymes throughout the food and not sufficient to sterilize or cook the food. The combination of mild heat treatment and freezing produces a product which will maintain its fresh color, taste and appearance after prolonged storage.
U.S. Pat. No. 2,619,424 of Masure discloses a process for preparing dehydrated carrots having improved storage qualities. The carrots are dehydrated, then moistened with water, optionally containing starch, and then the carrots are dehydrated to a moisture level below about 10%. The use of starch assists in preserving the color of the final product although the absorbed water is the primary factor in improving the stability of the color and the carotene content.
It is an object of this invention to prolong the post harvest life of the fresh root crops.
It is another object of this invention to improve the shelf life of fresh carrots.
It is a further object of this invention to provide raw carrots in a ready-to-eat form and to improve the shelf life of these fresh carrots.